Bus-Bro is correct --- if you have access to a little wire fed mig welder, that's the way to go. But they are very easy to learn, use and dial in for sheet metal. I must have filled in over a hundred various sized holes in my floor with one. Sealants and goo are gonna go away over time and the larger the hole, the more likely all the work you put on top of it will be exposed to water & road grime from below. To my mind, now is the time to do it right and forget it for another 65 years (that's how old my floor is).
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